(1) Field of the Invention
This invention relates to chemical finishing processes for textiles. More particularly it relates to catalysts for treatment of cellulose-containing textile materials with crosslinking agents to produce easy-care properties.
(2) Description of the Prior Art
It is well known that smooth drying appearance and wrinkle resistance of cellulose-containing textiles can be enhanced by suitable treatment of such materials with certain chemical agents. The chemical agents employed in such treatments generally require catalysts to affect reaction with the cellulosic components to achieve improvement of the desirable properties in the finished products. Consideration of strength losses and formaldehyde release have limited the scope of catalysts acceptable in finishing operations. Those catalysts widely employed in the processing of textiles for durable-press, for instance, are not normally useful in other processes.
Sulfur acids such as hydroxymethanesulfonic, methanesulfonic, and para-toluenesulfonic have been cited for their use as catalysts in durable press finishing. These are strong acids capable of promoting crosslinking in cotton with a high degree of efficiency. However, because they are strong acids, careful control in finishing must be maintained so as to avoid severe damage to the physical properties of the treated fabrics. Even with this careful control and use of these acids, treated fabrics have tearing and breaking strength retention values much lower than desired. It is also known from work by Andrews, Harper, and Vail (Textile Research Journal, Vol. 50, pages 315-322, May 1980) that Bronsted acids, such as the sulfonic acids mentioned above, catalyze the crosslinking reaction and, if not completely washed out after finishing, catalyze the reverse reaction (hydrolysis of crosslinks) to release odiferous formaldehyde. Also taught by Andrews, Harper, and Vail (op. cit.) is the knowledge that Lewis acids also are capable of catalyzing the crosslinking reaction but are not as hydrolytically active as the Bronsted acids. Mixtures of these two types of catalysts are known to those skilled in the art as mixed catalysts. One of the more widely used of these mixed catalysts is the mixture of magnesium chloride and citric acid. A synergistic effect from this combination is such that higher durable-press ratings result than can be produced from either component by itself from a given set of finishing conditions. However, this synergistic effect of catalyzing the crosslinking reaction also applies itself to the hydrolysis or reverse reaction in which decrosslinking or promotion of formaldehyde release occurs.
An ideal catalyst would be one which is acidic enough to promote the crosslinking reaction but is not so acidic as to severely weaken the fabric during finishing. Also, this same catalyst must not after finishing be capable of reversing these crosslinks and promote formaldehyde release. Thus, the theory that any acid will do in catalysis of durable press finishing must be flawed. Researchers in catalysis have tried to show why certain catalysts are better than others, and if not better overall, than at least better for a specific application.
Salts of strong acids, and in particular, ammonium salts, such as ammonium chloride have been used as catalysts because they are the combination of a strong acid and a weak base. Hydrolysis of such salts produces an acidic solution.
There are also organic compounds which contain both acid and basic moieties. Dependent upon the strength of these acidic and basic moieties, these compounds are capable of attracting or releasing protons. Such compounds are known as zwitterions. In much the same manner as the inorganic ammonium salts hydrolyze to produce an acidic solution, the solubilization of zwitterions which contain an amine group and a strongly acidic group such as sulfonic, sulfinic, phosphinic, phosphonic, and multiples thereof also produce an acidic solution. Acidic amino acids, that is compounds which contain fewer amino groups than carboxyl groups are also included in this class of compounds, zwitterions.